On bumpy tracks you see your legs wobbling as if you've got St Vitus' Dance. Your eyes vibrate so much you can't focus

Driving in a Grand Prix is like sitting inside a 200mph tubular vibro-massage machine for an hour and a half, while simultaneously working with weights in a gym.

The cockpit is your office and to survive, mentally as well as physically, you obviously need to be completely comfortable. My Sau-ber-Ford has a specially tailored seat made by Pro Seat. They use a process of bagging polystyrene beads and then gently withdrawing the vacuum from the bag once I'm sitting comfortably on it. This creates a template for my race seat. You get thrown around more than a cowboy in a rodeo, laterally and fore and aft, so you've got to have support.

You're strapped in tightly, of course, but even then you move around a lot, so while your shoulders and hips might stay in place, you need to protect your torso and thighs. On really bumpy tracks you can look down and see your legs wobbling as if you've developed St Vitus' Dance. Your bum is on the seat and your feet are on the pedals, but the bits in between seem to get a spaghetti-like life of their own!

It's also important to sit properly. Sit too high and you interfere with airflow into the engine, while if the windscreen is too low your head gets buffeted so much that you cannot see where you are going. Your eyes can vibrate so much in their sockets that you cannot focus. You have to concentrate so hard just to see where you're going that you get drained physically.

If you get your cockpit ergonomics right, you will not have a problem with breathing, or with cramp or fatigue. Things like seat shape and throttle position really are extremely important.

Downforce is a wonderful thing, but it has its price. The tyres generate a lot of grip and, with around a tonne of downforce in the very high G corners, everything gets very loaded up. That makes the steering effort very, very heavy.

You do not quite get to the point where you can't turn the wheel, but it certainly feels like it sometimes, especially at circuits like Suzuka. That's what you train for in the gym.

You are over 1G most of the time, but you can get as high as 3.5 or 4G under braking, and almost that high in the very fastest corners, like the first part of Becketts at Silverstone. That means you weigh four times your normal weight, and that's why it's so important to get muscular stamina. You can do a lot in the gym, but the only real training for this is driving itself. It's the only way to fine-tune your muscles, because G forces tend to expose any weak points you didn't exercise in the gym.

A Formula One car cockpit is also like a Turkish bath, so imagine sitting in one of them for an hour and a half. The temperature can get over 100F. You feel some heat from the side-mounted water radiators, plus you've got your three-layer driving suit and another layer of flameproof underwear. The screen is designed to flick air over your head and into the engine's airbox, so precious little heat actually gets sucked out of the cockpit itself.

Your body is always being banged about one way or another, either laterally or fore and aft, or a combination of these. You never stop moving around, and you are always being hammered.

A footballer can sprint down the wing and make a cross, then trot back. He has time to rest and recover. We do not. In the car it's just you, and there's a much higher concentration. You are also making a much higher physical outlay. Driving a Grand Prix is like going into a gym and for two hours just going flat-out from one machine to another without a break. Non-stop. That's all great for getting muscles toned, but then the shocks come later, the jolts and bangs.

And, of course, the odd accident. Those where your body twists on impact are the worst, like my old Lotus team-mate Mika Hakkinen had in Adelaide last year. That was a very big hammering.

The only way you would get any real idea in your road car of what driving a Formula One car feels like would be if you drove head-on into a wall. That's what it feels like when we brake really hard. But I'm sure you'd rather not go to those lengths.

Mentally you know you've done something damn difficult when you get out of the car after a race, but when you win, as I discovered for the first time at the British Grand Prix at Silverstone last year, it's one of the greatest highs in the world. Adrenalin and euphoria just massage away all the negative feelings.